1. Field of the Invention
The present invention relates to an improved volume-reducing solidification treatment of radioactive waste water containing boron primarily as boric acid or borates.
2. State of the Art
At nuclear power facilities, especially PWR type plants generating radioactive waste water containing boron primarily as boric acid, or borates, where solidification with the cement has been conducted, the waste water is evaporated and concentrated and as much as possible of the solid component is mixed with a cement paste in order to meet requirements in recent years for as high a degree of volume reduction as possible.
However, the following two problems exist with volume-reducing cement solidification. Boron primarily as boric acid or borates is dissolved in the waste water, and:
(1) during the evaporation and concentration process the boric acid or borates crystallizes, causing problems during the concentration operation; PA1 (2) when the concentration of boric acid ions in the cement increases, hydration reaction of the cement is hindered and a satisfactory solidified product can not be obtained.
Concerning the first problem, by adding caustic soda to the waste water the boric acid is converted to sodium salts thereof and solubility of the boron compound is raised. At the same time, this also serves as an acid neutralization treatment of the waste water. But, to avoid crystallization of sodium salts, there are limits to the degree of concentration attainable.
Measures to render the boric acid insoluble are possible in order to solve the second problem.
In the solidification treatment of radioactive waste water the prior art includes a cement solidification method (Japanese Patent Disclosure No. 54- 145900) which also uses asbestos fibers, in which dissolved matter is made insoluble, forming a stable suspension which is concentrated. This method discloses the use of lime or baryta to render the boric acid in the liquid insoluble.
However, in a method such as this, when, for example, lime is added to render the boric acid insoluble, minute fibrous matter preciipitates, the liquid becomes thixotropic or sensitive to vibration, and is extremely difficult to handle. The liquid will maintain a paste-like state when agitated and when agitation is stopped it will change into a gel.